1. Field
One embodiment of the invention relates to a gradation control apparatus and a gradation control method which are for images including many moving image components.
2. Description of the Related Art
In recent years, a television (TV) receiving apparatus which receives digital broadcasts has become popular. The TV receiving apparatus extracts a desired packet from a transport stream and decodes the compressed digital video signal in the packet.
The digital video signal is compressed by the MPEG method. When the video signal is decoded, block noise may occur. A coring technique has been proposed which extracts the pixel difference between fields or frames of the digital video signal, determines moving image components, and adaptively controls the noise reduction level according to the determination result (e.g., refer to Jpn. Pat. Appln. KOKAI Publication No. 2007-53697). In the coring control, moving image components are detected from the video signal and the amount of coring (or the noise reduction level) is changed according to the detection level. The degree of moving images is determined by, for example, detecting the histogram of information on the difference between frames and determining the number of pixels not less than a certain level.
Furthermore, the technique for performing a smoothing process on a video signal plain region has also been proposed (e.g., refer to Jpn. Pat. Appln. KOKAI Publication No. 2008-160440). It is known that the technique has the effect of reducing stripes or block noise due to the deterioration of gradation.
However, with the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2008-160440, if the noise reduction effect is increased too much, an image whose degree of moving image is low becomes blurred on the whole.